Process of producing all skin rayon



United States Patent @fiice Z,890,l30 Patented June 9, 1959 PROCESS OF PRODUCING ALL SKIN RAYON John A. Howsmon, Wilmington, Del., assignor to Ameri= can Viscose Corporation, Philadelphia, Pa., a corpsration of Delaware No Drawing. Original application June 29, 1955, Serial No. 519,000. Divided and this application June 24, 1957, Serial No. 667,669

4 Claims. 11. 106-165) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the, viscose solution is allowed to ripen and issubsequently extruded through a shaped orifice into a suitable coagulating and regeneratingbath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous-acid solution containingzinc sulfate. The filament may subsequently be passed through a hot aqueous bath Where it is stretched to improve its properties such as tensile strength. The filament may then be. passed through a dilute. aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it isnot completely regeneratedupon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations andv drying being collected either before or after these treatments.

h me as o m d y the co ntion m q consist of a skin or outer shell portion and a core portion with a sharp line ofdemarkation between the two. The cross-section of the filaments exhibits a very irregular or cren-ulated exterior. surface when even small amounts of zinc salts orv certain other polyvalent metal salts are p e e n he innin ba Th s in an o o t of the filament represent ditferences in structure and these different portions-possess dilferent swelling and staining characteristics, the latter permitting a ready identification of skin and core The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a 'lowabrasionresistance and a low flexlife, is subject to fibrillation andis relatively stilt.

It hasnow been discovered that the presence of small amounts of alkali-solublealkylene oxide adducts of cresol in viscose results in the production of shaped bodies of regenerated cellulosesuch as filaments, films, sheets and the like composed of all skin andhaving improved properties andcharacteristics providing that the amount of the adduct is maintained'within certain limits and the composition of =the spinning bath is maintained within certain composition limits which will be defined hereinafter. Themqstrsa y.disting ishab e;char c i t cs a 2 compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely or" skin.

This invention contemplates the use of such compounds as are more technically classed as polyoxyalkylene glycol ethers of cresol such as, for example, the ethers of ethylone and propylene glycols and cresol. The adducts or ethers may be derived from the o-, mor p-forms of cresol or from the commercial grades of cresol which consist of a mixture of all three forms or from the commercial cresylic acid which is the high-.cresol-containing fractions distilled from coal tar. The adducts may consist of a mixture of ethers having polyalkylene oxide chains of different length or having polyalkylene oxide chains of substantially the same length. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and in alkali solutions such as a 6% caustic solution, the polyoxyethylene glycol ethers or ethylene oxide adducts of cresol are preferred. Accordingly, the invention will be illustrated specifically by reference to the polyoxyethylene glycol ethers of cresol.

The polyoxyethylene content of the adducts or ethers should contain an average of at least 4' ethylene oxide units per molecule of cresol, and may be as high as 50 to units, however, there appears to be a tendency of unstability with the higher number of ethylene oxide units. The preferred ethers contain from about 6 to about 25 ethylene oxide units per molecule of cresol. The adducts or ethersv may be conveniently added to the viscose in the form of av solution in water or in a caustic soda solution.

The amount of the adduet which is incorporated in the viscose must be at least about 0.25% by weight of the cellulose in the viscose and may vary up to about 3.5% to 4%, preferably, the amount variesfrom 0.5% to 2%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The adduct may be added atany desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or. after filtration. The adduct is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 6% to about 8% cellulose, the particular source of the cellulose being. selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose containing the small amount of the adduct, may have a sodium chloride salt test above about 7 and preferably above about 9 at the time of spinning or extrusion.

In order to obtain the improvements. enumerated hereinbefore, it is essential that the composition of the spinningbath be maintained within. a well defined range. presence of. the alkylene oxide adducts of cresol in the viscose combined with these limited spinning baths resultsin the production of yarns of-improved properties such as. highv abrasionresistance, highfatigue resistance and consisting of filaments composed entirely. of skin.

Generically and in terms of the industrial art, the spin ning bath is a low acid-high zinc spinning bath containsi q abou to a o 5% dium s lfate and from about 3% to about zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may very from about C. to about 80 0., preferably between about C. and about 70 C. As is well known in the'conventional practice in the art, certain of the physical properties such as tensile strength 'vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about C. and C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is lust above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is sufliciently rapid to form a filament having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufiiciently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the all skin products from a 8% cellulose, 7.5 caustic-viscose and containing the adducts lies between about 6.5% and about 8.7%. The acid con- 'centration may be increased as the amount of the modifier is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of modifier and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount ofthe adduct is increased beyond about 4%, while other conditions are maintained constant. For example, a viscose containing about 8% cellulose, about 7.5 caustic soda, about 35% (based on the weight of cellulose) carbon disulfide, and 1% (based on the weight of cellulose) of an ethylene oxide adduct of cresol and having a salt test of about 9 when extruded into spinning baths containing 16 to 20% sodium sulfate, 4 to 8% zincsulfate and sulfuric acid not more than about 8.6% results in the production of all skin filaments. Lesser amounts of sulfuric acid may be employed. Greater amounts of sulfuric acid result in the production of products having skin and core. A lowering of the amount of the modifier, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. It has been determined that the maximum concentration of acid which is permissible for the production of all skin products is about 9%.

The presence of the alkylene oxide adducts of cresol in the viscose retards the coagulation and, therefore, the amount of modifier employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above.- and at a spinning speed of about 50 meters per minute, the modifier is employed in amounts within the lower portion of the range, for example, about 0.75%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufiieient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufiicientso that the filaments will not adhere to each other as they are brought together and withdrawn from the bath. c

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about -to about 120%, preferably between and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. It is to be understoodl that the invention is not restricted to the production of filaments and yarns but it is also applicable to other" shaped bodies such as sheets, films, tubes and the like.- The filaments may then'be passed through a final re-' generating bath which may contain from about 1% to" about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath,

. or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleach ing and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of alkylene oxide adducts of cresol and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics. are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity .in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Flaments prepared from viscose containing alkylene oxide adducts of cresol have superior abrasion and fatigue resisance characteristics and have a high flex-life. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose modified with an ethylene oxide adduct of cresol (commercial mixture of o-, mand p-cresol) containing an average of about 8 ethylene oxide units per molecule of cresol, the viscose containing about 8% cellulose, about 7.5% caustic soda, and having a total carbon disulfide content of about 35% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 35% carbon disulfide based on the weight of the cellulose and chuming for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. The desired amount lulo se) of the ethylene oxide adduct of cresol was added to incorporated in the viscose as described above. The viscose employed in the spinning of filaments had a salt test of 14.5. The viscose was extruded through ,a spinneret to form a 200denier, 120 filament yarn at a rate of about 22 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60. C. and contained 8.7% sulfuric acid, 8% zinc sulfate and 18% sodium sulfate. The yarn was stretched about I 82 while passing through a hot water bath at 95 C. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments hayea smpotln non-crenulated exterior surface and consis t entirely of skin, no core being detectable at high magnification (e.g. 1500 The filaments of a control yarn spun with the same viscose but without the addition of the modified agent and spun under. the same conditions, exhibit a very irregular and serrated surface and are composed of about 70% to 75 skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 2 To a viscose as described above, there was added 0.5% (based on the weight of the cellulose) of the ethylene oxide adduct of cresol. The viscose had a salt test of 13 and was spun into a 200 denier, 120 filament yarn by extrusion into a spinning bath containing 8.2% sulfuric acid, 8% zinc sulfate and 18% sodium sulfate. The bath was maintained at 60 C. and the extrusion rate was about 22 meters per minute. The filaments were subsequently passed through a hot water bath at 95 C. and stretched about 82%. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments were readily distinguishable from control filaments in that they have a smooth, noncrenulated surface and consist entirely of skin while the control filaments have a very irregular and serrated surface and consist of about 70% to 75% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 3 To a viscose solution as described above, there was added 0.5 (based on the weight of the cellulose) of the ethylene oxide adduct of cresol. The viscose had a salt test of 9.3 and was spun into a 200 denier, 120 filament yarn by extrusion into a bath containing 8.5% sulfuric acid, 8% zinc sulfate and 17% sodium sulfate. The bath was maintained at a temperature of 60 C. The extrusion rate was about 22 meters per minute. The water bath was maintained at about 95 C. and the filaments were stretched approximately 82% while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments were readily distinguishable from control filaments prepared from viscose containing no modifier in that they have a smooth, non-crenulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of about 70% to 75% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 4 To a viscose solution, prepared as described above,

there was added 1% (based on the weight of the cellu lose) of the ethylene oxide adduct of cresol. The viscose had a salttest of 13.6and was spun into a 200 denier, 120 filament yarn by extrusion into a bath containing 8.4% sulfuric acid, 8% zinc sulfate and 18% sodium sulfate. The bath was maintained at a'temperature of about 60 C. The extrusion rate was about 22 meters per minute. The water bath 'was m tainedat a temperature of about 9 n h filemen swe e st c ed 2% while p sing through the hot-water. The yarn was collected in a spinning box, washed free 'of acid and salts and dried.

The individual filaments were readily distinguishable from control filaments prepared from viscose containing no modifier in that they have a smooth, non-crenulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of bo t to ski a d t bal e ore i a sharpline of demarkation between the skin and the core. Other characteristics are set forth in the table which follows:

Tenacity, grams Elongation,

per denier percent Skin, per- I can Wet Dry Wet Dry Example 1 2. 3 3.0 26 21 100 Example 2- 2. 4 3. 2 3O 23 100 Example 3- 2. 5 3. 3 29 21 100 Example 4 2. 4 3. 2 27 21 100 Control 2. 3 3. l 28 22 70-75 Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit improvements in tenacity and elongation, however, the products consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to form about 65% to about for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The alkylene oxide adducts of cresol may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The modifying agent may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the cresol derivatives at the time of spinnlng.

If desired, small amormts of the modifying agent may be added to the spinning bath. Since the modifying agents are water-soluble to some extent, some of the modifier will be leached from the filaments and will be present in the bath.

The term cresol is used herein and in the claims in a generic sense to include the pure forms of cresol, the commercial grades of cresol containing a mixture of the three isomers and such commercial grades as the coal tar fractions which are predominantly a mixture of the three isomers and are in some instances termed cresy-lic acid.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS cone. (General Dyestufis Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more'baths composed of 10% water and 90% dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

This application is a division of my copending application Serial'No. 519,000, filed June 29, 1955, now abandoned.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A viscose spinning solution containing from about 0.25% to about 4%, based on the weight of the cellulose in the viscose, of an alkali-soluble polyoxyalkylene glycol ether of cresol selected from the group consisting of V 8. alkali-soluble polyoxy-ethylene glycol ethers of cresol and alkali-soluble polyoxypropylene glycol ethers of cresol.

2. A viscose spinning solution as defined in claim 1 wherein the ether is a polyoxyethylene glycol ether of cresol.

3. A viscose spinning solution containing from about 0.5% to about 2%, based on the weight of the cellulose in the viscose, of a polyoxyalkylene glycol ether of cresol containing from 6 to about 25 alkylene oxide units-per molecule of cresol, the glycol ether of cresol being selected, from the group consisting of alkali-soluble polyoxyethylene glycol ethers of cresol and alkali-soluble polyoxypropylene glycol ethers of cresol.

4. A viscose spinning solution as'defined in claim 3 wherein the ether is a polyoxyethylene glycol ether of cresol.

References Cited in the file of this patent UNITED STATES PATENTS 20 2,145,527 Polak et al. Jan. 31, 1939 2,451,558 Schlosser et al Oct. 19, 1948 FOREIGN PATENTS 1,105,329 France Nov. 29, 1955 

1. A VISCOSE SPINNING SOLUTION CONTAINING FROM ABOUT 0.25% TO ABOUT 4%, BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, OF AN ALKALI-SOLUBLE POLYOXYALKYLENE GLYCOL ETHER OF CRESOL SELECTED FROM THE GROUP CONSISTING OF ALKALI-SOLUBLE POLYOXYPROPYLENE GLYCOL ETHERS OF CRESOL. ALKALI-SOLUBLE POLYOXYPROPYLENE GLYCOL ETHERS OF CRESOL. 